In the Third Age, the Orcs of Angmar claimed it as their capital, which was one of the reasons for the Dwarves' special hatred of this people. After the fall of Angmar Gundabad remained an Orc stronghold, until it was cleaned of Orcs during the War of the Dwarves and Orcs. But it is likely that the Orcs repopulated it over the next two hundred years, although there probably weren't as many.